Extraneous Conductive-part

[Michaelwgroves]

I've had my work assessed which has raised a question about Extraneous-conductive-part. I just want to be sure I fully understand this.
BS7671 Part 2 defines it as; A conductive part liable to introduce a potential, generally Earthed potential, and not forming part of the electrical installation.
e.g. A conductive part; liable to introduce potential; and not forming part of the electrical installation.

The installation is a studio flat. There is no gas, the mains water is supplied from the road in plastic throughout. The stop cock is plastic. On from this is plastic pipework terminated under the sink. Under the sink is a 3KW water heater and some copper pipework. The pipework leaving the sink cupboard is plastic. Therefore the full extent of copper pipework is under the sink.
It is a new installation protected by RCD. It is not a special location (7)
I do not require "Supplementary equipotential bonding" as it is not Part 7 and ADS is satisfactory.

My question(s) are;
Am I correct in identifying this as an Extraneous-conductive-part ?
Guidance Note 8 advises if the measured resistance between the Extraneous-conductive-part and MET is greater than 6.67k ohms it need not be considered Extraneous-conductive-part. I'm gonna take this measurement tomorrow, assuming it is higher can I conclude I do not need to bond?

However, contrary to this;
Guidance Note 8 states; It is important to note that protective equipotential bonding is always required where the protective measure is ADS.
Guidance Note 8 shows Extraneous-conductive-part with main Protective equipotential bonding.
So having gone around the houses I conclude I have to bond the Extraneous-conductive-parts with 10mm.

So trying to make sense of this, if Extraneous-conductive-part is close to electrical installation and could become live, bond it. If its in middle of field take reading and only bond if below 6.67k ohms?

Is my summary correct, if not please correct me.........

 

[Pete999]

I've had my work assessed which has raised a question about Extraneous-conductive-part. I just want to be sure I fully understand this.
BS7671 Part 2 defines it as; A conductive part liable to introduce a potential, generally Earthed potential, and not forming part of the electrical installation.
e.g. A conductive part; liable to introduce potential; and not forming part of the electrical installation.

The installation is a studio flat. There is no gas, the mains water is supplied from the road in plastic throughout. The stop cock is plastic. On from this is plastic pipework terminated under the sink. Under the sink is a 3KW water heater and some copper pipework. The pipework leaving the sink cupboard is plastic. Therefore the full extent of copper pipework is under the sink.
It is a new installation protected by RCD. It is not a special location (7)
I do not require "Supplementary equipotential bonding" as it is not Part 7 and ADS is satisfactory.

My question(s) are;
Am I correct in identifying this as an Extraneous-conductive-part ?
Guidance Note 8 advises if the measured resistance between the Extraneous-conductive-part and MET is greater than 6.67k ohms it need not be considered Extraneous-conductive-part. I'm gonna take this measurement tomorrow, assuming it is higher can I conclude I do not need to bond?

However, contrary to this;
Guidance Note 8 states; It is important to note that protective equipotential bonding is always required where the protective measure is ADS.
Guidance Note 8 shows Extraneous-conductive-part with main Protective equipotential bonding.
So having gone around the houses I conclude I have to bond the Extraneous-conductive-parts with 10mm.

So trying to make sense of this, if Extraneous-conductive-part is close to electrical installation and could become live, bond it. If its in middle of field take reading and only bond if below 6.67k ohms?

Is my summary correct, if not please correct me.........

This any help?

 

[Michaelwgroves]

Perfect, I'll take readings tomorrow while I'm on site tomorrow.

Thanks,

 

[Wilko]

Thanks Pete for the vid, it clarified it nicely. In the past I have bonded everything left right and centre

 

[Midwest]

There is a slight caveat, reg 528.3.4, electrical services in close proximity to non electrical services. Don't think would apply in your circumstances, but would in an installation with plastic incomer & metal internal services.

 

[Michaelwgroves]

I've now been to site and taken the reading. The pipework to earth is 6.8k ohms. Therefore as per Guidance Note 8 it is not an extraneous-conductive-part.
However, as per the video above as it is above 1667 ohms it requires bonding. So we have an impasse......

My assessors view as per regs, it is an "installation and locations of increased shock risk" This is because the pipe work is right next to electric water heater. Therefore there is a risk if the heater went faulty the pipework could become live. Without knowing the installation this sounds practical. However, the water heater is fully enclosed in a plastic case and the connections have dielectrics on them, thus fully insulating the unit from the pipework. Hence why there is such a high reading to earth.
It's not a big deal adding supplementary bonding; so I've done it regardless, but I still want to ensure my understanding is correct going forward.
My thought is you would need to purposely go out of your way to make this live, it just could not happen by fault.
I questioned why we would not bond the sink, the assessor said he would because of the heater. Any current using equipment next to an extraneous-conductive-part should be bonded.

I'm struggling to find anything in the regs to back this up, to me it's just a lump of metal in the vicinity, just like the door hinges....

Any pointers would be appreciated......

 

[Midwest]

I'm struggling to understand how this piece of pipe can be thought of as an extraneous conductive part, regardless of it's resistance to earth.
My understanding is bonding to extraneous conductive part, is reg. 411.3.1.2 or supplementary equipotential bonding reg. 701.415.2 or proximity to services reg 528.3.4. A piece of metal pipe, under sink sandwich between plastic pipe, does not IMO come under the definition of extraneous conductive part.

As regards bonding a metal sink, because of proximity to current using equipment, well.... think your assessor has been reading a 15th instead of 17th edition. The water heater, presumably has a cpc connection. Would the assessor recommend bonding aluminium windows?

PS not having a go at you, but questioning your assessor? Who is she/he?

 

[Pete999]

I've now been to site and taken the reading. The pipework to earth is 6.8k ohms. Therefore as per Guidance Note 8 it is not an extraneous-conductive-part.
However, as per the video above as it is above 1667 ohms it requires bonding. So we have an impasse......

My assessors view as per regs, it is an "installation and locations of increased shock risk" This is because the pipe work is right next to electric water heater. Therefore there is a risk if the heater went faulty the pipework could become live. Without knowing the installation this sounds practical. However, the water heater is fully enclosed in a plastic case and the connections have dielectrics on them, thus fully insulating the unit from the pipework. Hence why there is such a high reading to earth.
It's not a big deal adding supplementary bonding; so I've done it regardless, but I still want to ensure my understanding is correct going forward.
My thought is you would need to purposely go out of your way to make this live, it just could not happen by fault.
I questioned why we would not bond the sink, the assessor said he would because of the heater. Any current using equipment next to an extraneous-conductive-part should be bonded.

I'm struggling to find anything in the regs to back this up, to me it's just a lump of metal in the vicinity, just like the door hinges....

Any pointers would be appreciated......

Look at 415.2.2 that may explain as well

 

[Wilko]

Hi - I take your point Midwest (#7) as the bit of pipe is wholly within the room and so it can't be extraneous, can it? Checking 'extraneous' in the dictionary and it gives 2 meanings, either irrelevant (not my pick) or external (my pick).

 

[Michaelwgroves]

Thanks for input guys, it's all good stuff. I think we are all saying the same thing, it can't be extraneous as it is internal and greater than 6.8K ohms.
I don't believe 415.2.2 is relevant at this stage as this deals with the effectiveness of supplementary bonding; therefore after the decision has been made to bond, but we are questioning that decision.
701.415.2 is specific to Locations containing a bath or shower, therefore not relevant.
411.3.1.2 is not relevant as we have already concluded it is not an extraneous-conductive-part.
528.3.4 Could be valid, albeit the wire is heat resistant and protected by RCD.
I've attached photo so you can better see the topic. This is the full extent of metal pipe work. As you can see Plastic mains supply and bathroom supply both in plastic bottom right. You can also see the dielectric on the hot supply which insulates the tank from the pipework.(Cold dielectric out of view).
So I can not see why this needs any form of bonding?

 

[Midwest]

Nope, I would not be bonding that. If you see any new bathroom/kitchen refurbishments, they will be a myriad of bits of plastic to metal to plastic to metal etc pipe connections, some of which you not would see and would not get bonded, and why would you?

Who is your assessor?

 

[Michaelwgroves]

We're on the same page, but I don't want to get into naming the assessor.

 

[Ian1981]

Can the copper pipe introduce an earth potential is the question?
As its plastic pipe feeding the copper, answer is no it's just isolated copper pipework.